Tandem electrocatalytic benzylic alcohol oxidation and aldol condensation for efficient valuable α,β-unsaturated ketone production

Abstract

α,β-Unsaturated ketones, crucial in organic synthesis and life sciences, are conventionally produced through aldol condensation of ketones and aldehydes. However, traditional synthesis methods involve high temperature, pressure, and the use of environmentally harmful solvents, hindering sustainable development. Herein, we present one-step electrosynthesis of benzylidene acetones and 2-methylenephenyl cyclohexanone via tandem reactions, by coupling electrooxidation of benzylic alcohols to the corresponding aldehyde, followed by aldol condensation between the aldehyde and the ketone. Selective formation of benzaldehydes is key to the tandem reaction and was achieved over a cubic oxide-supported gold catalyst (Au/CuO) as the anode, showing the ability to adsorb benzylic alcohols and generate the active adsorbed oxygen species (OH*) for selective oxidation. The tandem reaction strategy demonstrates its versatility in the synthesis of α,β-unsaturated ketones from benzyl alcohols with different substituents and acetone/cyclohexanone. As proof of concept, we constructed a flow electrolyzer and achieved continuous electrosynthesis of benzylidene acetone coupled with H₂ production at ampere-level current, delivering a benzylidene acetone productivity of 9.5 mmol h⁻¹ and a H₂ productivity of 0.4 L h⁻¹. This study demonstrates the potential of coupling electrocatalysis and thermocatalysis in tandem, with implications for synthesis of more value-added chemicals.